Abstract

There is increasing evidence that cAMP promotes the relaxation of the myometrium, and other types of smooth muscle via the activation of cAMP-dependent protein kinase and other intracellular signalling pathways. The data from the first part of this study show that cAMP reduces the expression of most of the labour-associated gene, such as oxytocin receptor (OTR) (via PKA) and FP receptor. Interestingly, cAMP induces COX-2 expression via MAPK pathway. Therefore, with the exception of the COX-2 data, these findings suggest that cAMP agonists have the potential to be effective tocolytic agents.Most researchers also believe that progesterone plays an important role in maintaining uterine quiescence throughout pregnancy by inhibiting the expression of contraction-associated proteins in the myometrium. However, the exact mechanism responsible for the progesterone-induced inhibition of labour-associated genes expression remains unclear. Clinically, progesterone treatment has been shown to reduce the risk of preterm labour (PTL) in high-risk populations. Surprisingly, progesterone had no effect on the occurrence of preterm labor in multiple pregnancies. So the second part of this project focused on the hypothesis that cAMP could enhance the myometrial response to progesterone. The combined effects of cAMP and progesterone on the activation of different pathways in primary cultures of human myometrial cells was studied. It was found that forskolin enhanced the progesterone-induced expression of genes such as FKBP5 and 11βHSD1. The forskolin effects included the up-regulation of progesterone receptor (PR)-B levels and enhanced progesterone-driven activity of a progesterone response element (PRE) as well as increased PR-B binding to the PRE. The data also show that forskolin attenuate the association between PR and NCoR. Knockdown of NCoR blocks the ability of forskolin to enhance progesterone driven PRE activity. Furthermore, the ability of progesterone to repress IL-1β-induced COX-2 expression was enhanced by forskolin, which was associated with a delay in IL-1β-induced nuclear phospho-p65 entry, as well as an increase in IκB synthesis and a reduction in NF-κB binding to the COX-2 promoter.Overall, these data identify important interactions between cAMP and progesterone pathways that control myometrial expression of labour-associated genes and point towards a novel role for cAMP agonists to supplement progesterone-based clinical protocols in the treatment of PTL.